Accomplishments: With the initial support (RO1 AA11321-01A1), we pioneered the concurrent application of magnetic resonance imaging (MRI), magnetic resonance spectroscopy at (MRS), and 1231-iomazenil single photon emission computerized tomography (SPECT) to characterize parallel changes in cortical GABA levels and GABA-A receptors during recovery from alcohol dependence (healthy subjects;patients at 1 week, 1 month, and 6 months of sobriety). Our SPECT data describe increased ligand binding to GABA-A receptors over the first week of sobriety that recovers during the next 3 weeks. These data could reflect a deficit in GABA-A receptor function normalizes with sobriety. Our MRS data indicate that cortical GABA deficts are not present in acute withdrawal, but levels declined over the first month of sobriety as ligand binding to GABA-A receptors dropped. We hypothesize that these shifts reflect a restoration of GABA-A receptor function that is mediated by changes in GABA-A receptor subunit composition. Comorbid smoking blocked the withdrawal-related changes in cortical GABA levels and GABA-A receptors. Thus, GABA systems may mediate a facet of the comorbidity of smoking and drinking. This renewal application would enable us to: 1) demonstrate that rapid time-dependent change in GABA-A receptors with sobriety occur within subjects, 2) replicate the reduction in GABA levels with sobriety using higher field (4.0 T) human MRS, and 3) replicate the protective impact of smoking. Analyses will control for tissue atrophy and GABA- related genotypes. Because GABA-A receptor subunit substitutions may contribute to changes in GABA-A receptor binding, we will relate SPECT binding data to changes in the GABA-related gene expression, including receptor subunits, using gene expression arrays applied to monocytes extracted from subjects at each imaging session.